Is it permissible for me to work as an architectural engineer in a private office, where I am alone with the owner of the office, a foreign man, for 15 to 30 minutes in the morning, with the door sometimes closed?

If the office is in a public place and there is no suspicion (of impropriety), then there is no harm in working there. However, seeking safety for one's religion is more preferable. If there is no dire need for this job, then look for another, seeking the pleasure of Allah, for whoever gives up something for the sake of Allah, He will compensate him with something better. This is based on the Almighty's saying: "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect." And based on the saying of the Prophet (peace and blessings be upon him): "Indeed, you will not give up something for the sake of Allah, the Mighty and Sublime, except that Allah will replace it with something better for you."